1. Field of the Invention
The present invention generally relates to an optical device capable of coupling or dividing light having at least three wavelengths, and in particular, to a wavelength division coupler including a directional coupler.
2. Description of the Related Art
In a bidirectional transmission/reception, each subscriber device or a central base station requires an optical transceiver, such as a three-wavelength division optical filter, capable of coupling or dividing different upward and downward light. The three-wavelength division optical filter has a structure in which a groove that cuts a portion where a two-branch waveguide is formed and an optical filter capable of selectively transmitting or reflecting a specific wavelength inserted into the groove. An arrayed waveguide grating may be used for the purposes of wavelength dividing or coupling process.
However, the volume of the arrayed waveguide grating or the three-wavelength division optical filter tends to increase in this type of application, and the optical filter experiences a loss depending on the coupling efficiency and the volume of the device. Moreover, when using the three-wavelength division optical filter or the arrayed waveguide grating, the operation process becomes complicated, and the cost of parts increases, thereby causing an increase in the manufacturing cost.